Families of serial killer Robert Pickton’s victims have known the answer to who killed their loved ones for years.

On Tuesday, the process aimed at understanding why he was able to do it, how he was able to conduct such a prolific killing spree for so long, will get under way.

The families have been calling for public hearings since before Mr. Pickton was arrested and eventually convicted of six murders. For them, the convictions represent a frustratingly small number of victims and belies the scale of his crimes and the failings of the police and justice system to stop him.

Mr. Pickton’s trial brought out the gruesome details of the killings themselves, but it only revealed what happened, not why.

Those answers are more complicated, and so too is the task of the Missing Women Commission of Inquiry, ordered by the B.C. government last year after Mr. Pickton’s final appeals were exhausted.

“The trial of Pickton just focused on his culpability, and not the quality of the police investigation. It didn’t address why it took so long to apprehend that murderer,” said lawyer Cameron Ward, who is representing the families of at least 17 of Mr. Pickton’s victims at the hearings.

“I think our society has the right and the need to determine why the investigation unfolded the way it did, and why, for so many years this man was allowed to prey on vulnerable women in the Downtown Eastside.”

CTV News reported on the weekend that Mr. Pickton was interviewed by commission counsel to determine if he should be called as a witness. However a commission source said Monday it is unlikely the serial killer will be called.

“To be thorough and comprehensive, the commission needs to explore all potential witnesses,” the source said, but refused to confirm if Mr. Pickton was interviewed. “We’re still interviewing witnesses. We haven’t prepared a formal witness list, I have to say it is highly unlikely that Mr. Pickton would be on our witness list.”

Mr. Pickton was arrested in 2002 and convicted of six counts of second-degree murder. The remains or DNA of a total of 33 women were found on his farm, and he bragged to police that he killed 49.

He lost his final appeal at the Supreme Court of Canada last summer, clearing the way for the public inquiry.

The public inquiry will examine the role of the Vancouver police and the RCMP, and why neither force was able to stop a serial killer – or even acknowledge that one existed – as sex workers vanished in the late 1990s and early 2000s.

The hearings will also look at the role of Crown prosecutors who, in 1998, decided not to charge Mr. Pickton with attempted murder after a sex worker was brutally assaulted at his farm a year earlier. Mr. Pickton remained free, and many of his victims were killed in the years that followed.

Some of the lawyers in the downtown Vancouver courtroom will almost certainly turn the focus on what advocates say are systemic problems that force impoverished, drug-addicted women into the dangerous sex trade in the first place.

Those issues aren’t specifically in the inquiry’s terms of reference. However, a set of less-formal hearings known as a “study commission” has already touched on some of them.

There will be allegations of negligence and wrongdoing, and lawyers for the families, the police, the government and others will argue about what changes are needed to prevent more vulnerable women from disappearing and dying.

“I’m not confident that sufficient lessons have been learned,” Mr. Ward said. “This was Canada’s most horrific mass serial murder, and nothing I’ve read so far has convinced me that something similar couldn’t happen again.”